Products utilizing electrical assemblies which generate an appreciable amount of heat, usually require that heat dissipation paths be designed in to prevent overheating of these assemblies. One popular solution is to locate a heat sink, such as a metal plate, at or near the site of the heat generating assembly, and providing a thermal path for heat to travel from this heat sink to other heat dissipating locations. For example, a relatively large power amplifier can be implemented on a substrate, and this substrate is mounted on a heat sink, and the heat sink is mounted on another substrate such as a printed circuit board. A heat dissipation path could be created by thermally connecting the heat sink to the frame or chassis of the host device. Leads provide the electrical connection between the substrate containing the power amplifier and the printed circuit board. Similar configurations are quite common in the art.
Despite some of the obvious manufacturing advantages of using leadless surface mountable assemblies, the use of leads has persisted to provide electrical connection between the assembly containing the heat generating electrical components and the general circuitry for the application. This results from the traditional design of placing the heat sink, which can be rather bulky, directly under the assembly, so that the electrical connections must be routed around the heat sink. Thus, leads are often used to accomplish this routing.
However, there are several problems which are inherent in the use of leaded electrical assemblies in the assembly of electronic circuitry. One such problem is that of lack of planarity, i.e., where the ends of the leads are not all on the same level or plane. Lack of planarity may prevent proper electrical connection between the component and the supporting substrate, thus affecting the ease of manufacture and the reliability of the assembly. Automatic placement of leaded components can also be difficult, depending on the size and orientation of the assembly, and hand placement may be necessary. Some applications, such as those involving wireless communications, require shielding of certain electrical assemblies to minimize electrical interference and spurious radiation emissions from the assembly. With leaded assemblies, the shields need openings to accommodate the leads, or alternatively, the shields need to be shaped to encompass the leads. Assuming the application is implemented on a printed circuit board (PCB), the PCB layout must accommodate these shields and this can reduce the space available for the other circuit components.
A further problem exists in current designs addressing the heat dissipation path between the electrical assembly and the chassis of the host device. When the assembly is mounted on the heat sink and the heat sink mounted on the printed circuit board, an excision is typically made through the printed circuit board to access the heat sink. This processing of the printed circuit board increases the number manufacturing operations and add to manufacturing costs. Moreover, an excision in the printed circuit board reduces the surface area available for electrical components, thereby increasing the product size.
The problems described thus far are particularly prevalent with the use of power amplifiers in the wireless communications industry. The packaging of high output power amplifiers or other high energy assemblies with large heat dissipation requirements have traditionally relied on leads to electrically connect the assembly to the printed circuit board. However, the demand for increase product quality, reduced manufacturing costs, and product miniaturization requires new solutions to the packaging design for these assemblies. As such, it is desirable to eliminate the leads for these electrical assemblies and to provide improved electrical performance in a smaller package, while maintaining the heat dissipating characteristics of prior art electrical assemblies.